The present invention relates to systems for purging particles and moisture from containers, and more particularly relates to a system suitable for purging moisture and potential wafer-contaminating particles from wafer cassette containers or pods used to transport semiconductor wafers in a semiconductor production facility.
A standardized mechanical interface (SMIF) system is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. Such a SMIF system is designed to reduce particle fluxes onto semiconductor wafers and/or reticles in a semiconductor production facility. The SMIF system prevents or minimizes particle contamination of the wafers during transport and storage of the wafers by ensuring that gaseous media surrounding the wafers is essentially stationary relative to the wafers, and further, by preventing exposure of the wafers to particles from the ambient environment.
The SMIF concept is based on the use of a small volume of motion- and contamination-controlled, particle-free gas to provide a clean environment for semiconductor wafers and other articles. Further details of one such system are described in a paper entitled,xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURINGxe2x80x9d, by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
SMIF systems are designed to prevent contamination by particles which range from below 0.02 xcexcm to above 200 xcexcm. Due to the small geometries of the components in modern semiconductor integrated circuits, particles falling within this size range can significantly adversely affect semiconductor processing. Current geometry sizes for semiconductor integrated circuits have reached less than half a micron, and those circuits are adversely affected by particles having a size as small as 0.01 xcexcm. In the future, semiconductor integrated circuits will be marked by increasingly smaller geometry sizes, requiring protection from contamination by correspondingly smaller particles.
In a typical SMIF system, semiconductor wafers are stored and transported in wafer cassette containers, or pods, and are transferred from the pod to processing equipment typically in the following manner. First, the pod is placed at the interface port of a processing tool. Each pod includes a box and a box door designed to mate with doors on the interface ports of the processing equipment enclosures. Then, latches release the box door, and the box door and the interface port door are opened simultaneously such that particles which may have adhered to the external door surfaces are trapped or sandwiches between the box and interface port doors. A mechanical elevator lowers or translates the two doors, with the cassette riding on top, into the enclosure-covered space. The cassette is transferred by gravity or a manipulator and placed onto the cassette platform of the equipment. After processing, the reverse operation takes place.
Another conventional method for transferring semiconductor wafers from a pod to a processing tool is shown in FIGS. 1-3 of the drawings, which illustrate side views of a SMIF arm cassette loading device 10. The SMIF arm cassette loading device 10 includes a base 11 which is supported on a floor or other supporting surface (not illustrated) in a clean room, and a frame 12 is upward-standing from the base 11. A pod support platform 14 is provided on the frame 12. A SMIF arm 13 is mounted on the frame 12 for bidirectional vertical displacement thereon, and a guide arm 17 for the SMIF arm 13 typically extends upwardly from the frame 12. Accordingly, a wafer pod 18, characterized by a cover 19 which is fitted with a removable bottom pod door 20 and contains a wafer cassette 21 that holds multiple semiconductor wafers 22, is initially placed on the pod support platform 14, as illustrated in FIG. 1. Next, a lifting mechanism (not illustrated) raises the SMIF arm 13 which, in turn, lifts the cover 19 from the removable pod door 20 in the bottom of the cover 19 as the cover 19 is detached from the pod door 20. The pod door 20 remains on the pod support platform 14 and continues to support the cassette bottom plate 23 of the exposed wafer cassette 21 thereon, as illustrated in FIG. 2. A robotic arm 16 then transfers the wafer cassette 21, still holding the semiconductor wafers 22, to an indexer 27, as illustrated in FIG. 3, which indexer 27 indexes the wafers 22 before loading them into the load lock 26 of a processing tool 25. After they are processed in the processing tool 25, the wafers 22 are transferred back from the indexer 27 to the pod support platform 14, as illustrated in FIG. 2. Finally, the SMIF arm 26 is lowered to lower the cover 19 of the wafer pod 18 onto the pod door 20 to again enclose the wafer cassette 21 and wafers 22, as shown in FIG. 1. The pod 18 is then transferred to another processing tool or a stocker either manually or by means of automatically-guided vehicles (AGVs) or overhead transport vehicles (OHTs) that travel on predetermined routes or tracks.
One of the problems associated with the foregoing type of SMIF arm cassette loading device 10 is that ambient air, moisture and some particulate impurities tend to become recaptured in the cover 19 of the pod 18 when the cover 19 is lowered back in place on the pod door 20 on the pod support platform 14. Resulting exposure of the wafers 22 to humidity, atmospheric air and foreign particles in the pod 18 during subsequent transfer to the next processing tool tends to induce corrosion and contamination of the wafers 22, as well as shorten wafer Q-time and adversely affect wafer yield performance.
Accordingly, an object of the present invention is to provide a system which is capable of purging atmospheric air, moisture and particles from an article-carrying container in a manufacturing or other facility.
Another object of the present invention is to provide an in-situ purge system which is capable of purging contaminants, moisture and ambient air from a wafer cassette container or wafer pod to increase the product wafer Q-time and yield performance of semiconductor wafers.
Still another object of the present invention is to provide an in-situ purge system which is capable of restoring a desired gaseous environment for semiconductor wafers on a water cassette inside a wafer cassette container or pod.
Another object of the present invention is to provide a method for the purging of moisture, ambient air and potential wafer-contaminating particles from a semiconductor wafer pod interior and restoring a normal clean gaseous environment inside the pod to minimize yield contamination and corrosion of semiconductor wafers transferred in a semiconductor production facility.
In accordance with these and other objects and advantages, the present invention comprises an in-situ purge system for charging the interior of a semiconductor wafer pod with nitrogen gas after the pod is exposed to ambient moisture, air and particles in a clean room. A gas supply line extends into the pod interior from a gas source, and a gas exhaust line extends from the pod interior to remove moisture, particles and excess gas from the pod interior as the pod contains a wafer-filled cassette and rests typically on a SMIF arm before transfer to a processing tool or other destination in the facility. The removable bottom door of the pod and the bottom plate of the cassette are modified to receive the gas supply line and the gas exhaust line.